Selective conversion of methanol into aromatic hydrocarbons over zinc-exchanged ZSM-5 zeolites

Abstract

The conversion of methanol into hydrocarbons over ZSM-5 zeolites has been studied with a special emphasis on improving the selectivity to aromatic hydrocarbons. The introduction of zinc or gallium cations to ZSM-5 appreciably increased the yield of or selectivity for aromatic hydrocarbons. Thus, under the reaction conditions of 700 K, methanol pressure of 40 kPa and W / F = 9.0g h mol-l, the yields of aromatic hydrocarbons over H-ZSM-5, Ga-ZSM-5, and Zn-ZSM-5 were 40.3, 48.2 and 67.4 YO, respectively. Over Zn-ZSM-5 the distribution of aromatic products on a molar basis was as follows; benzene (5.8%), toluene (28.O%), xylenes + ethylbenzene (45.6 %) and C9+(20.6 Yo). The reaction conditions were optimized to obtain the highest yield of aromatic hydrocarbons over Zn-ZSM-5. The yield of aromatics increased with temperature up to 700 K, but a further temperature increase led to the decomposition of methanol to carbon oxides. The selectivity for aromatics gave a maximum of 70% at a methanol partial pressure of 22 kPa. The yield of aromatic hydrocarbons increased with the degree of cation-exchange of H-ZSM-5 with Zn-cations, indicating the essential role of zinc species in the enhancement of the selectivity to aromatics. It is concluded that the zinc species has a capability of efficiently converting alkene intermediates to aromatic hydrocarbons.

Dimethyl Ether as a Source of Reactive Species for Alkylation of Benzene

“…As regards the details of this complex process and the reaction intermediates different views have been expressed. The formation of free carbene radicals [34], trimethyloxonium and ylide intermediates [37], carbocations [35] and surface methoxy species has been suggested [38]. FTIR spectroscopic studies on the interaction of DME with various solids confirmed that in the activation of DME by the acidic sites of oxides and ZSM-5 zeolites adsorbed methoxy and methyl species…”

“…In the interpretation of this finding we have to take into account the reaction pathway of DME. The conversion of DME to olefins (DTO process) is closely related to the methanol to olefins (MTO process) [16,[33][34][35][36][37][38][39][40][41]. The key step in both cases is the formation of C-C bond.…”

Co-cracking of bio-oil model compound mixtures and ethanol over different metal oxide-modified HZSM-5 catalysts

“…To further improve the selectivity of 28 aromatics, the influences of different metal oxides loaded onto HZSM-5 were investigated and a range of 29 model compounds were selected and mixed to simulate the distilled fraction of bio-oil. Two model 30 compound mixtures (MCM) were used for co-cracking with ethanol: (1) MCM-1 that contains hydrox- 31 ypropanone, cyclopentanone and acetic acid and (2) MCM-2 that contains hydroxypropanone, cyclopen- 32 tanone, acetic acid, phenol and guaiacol.…”

“…However, the selectivity 117 for C 3 -C 4 hydrocarbons was also high, which shows great potential 118 for an increase in the yield of aromatic hydrocarbons by promoting 119 aromatization during the cracking process. 120 In the methanol to gasoline (MTG) process, metal oxide-modified and Zn on the HZSM-5 both promoted the aromatization [28]. In Brunauer-Emmett-Teller (BET) method, and the external and 161 micropore specific surface areas were determined by t-plot method.…”

Effect of γ-alumina as active matrix added to HZSM-5 catalyst on the aromatization of methanol

“…Likewise, gallium modified HZSM-5 catalyst also had a capability of considerably elevating the selectivity towards aromatics [13][14][15][16], however, due to its high price, gallium was not appropriate for commercial application. In addition, zinc modified HZSM-5 catalyst was also widely reported in large numbers of papers [17][18][19][20][21][22][23][24], but the activity of the catalyst was unable to last long.…”